Only a fool could be confident what President Donald J. Trump’s next move will be. It’s not clear he knows himself.

But they say all politics is local, and would-be fortune tellers could do worse than look at US opinion polls, which show support for Trump – and the war – is tanking.

With November’s mid-terms threatening to overturn his narrow majority in Congress, the survival of Trump’s presidency is now at stake.

Expecting Americans to pay more than $4 a gallon in an election year is political suicide, but this is very much what’s being asked in the Republicans’ mid-Western heartlands where, thanks to Iran’s stranglehold over the Strait of Hormuz, the price of ‘gas’ has soared.

Trump needs a solution – and fast. Because without one, he can’t bring world energy prices down – or drive his poll numbers back up. This, remember, is a president elected on a specific promise to bring down the cost of living.

With peace talks stalling, there seem few options left for him.

Yesterday, in yet another surprise, Trump announced that America would play the mullahs at their own game and blockade Iranian oil.

We’ll see. Blockades don’t work quickly – if they work at all. And it’s unlikely that China, one of Iran’s main customers, would take this threat to its oil supplies lying down.

Besides, there’s a more immediate problem, which is that blockading Iranian exports would be yet another blow to the fragile world economy, and would drive the price of gas and fertiliser to even greater heights – the very outcome Trump is desperate to avoid.

A return to bombing seems more probable. Yet missiles have failed to bring about most of Trump’s stated objectives until now and seem unlikely to do so in the future.

It’s true the Pentagon has killed a generation of Iranian leaders and claims to have hit strategic targets such as missile factories.

Yet Iran appears to have more rockets, drones and launchers than the US originally thought.

If they survived 40 days of intense bombing, it means they could probably last another wave of attacks into the summer – which is far too late for Trump.

Besides, American voters won’t accept the true price of crushing the Islamic Republic’s resistance, which entails a ground invasion and US body bags.

Trump could certainly strengthen his hand by pressing Israel to stop bombing Hezbollah, Iran’s ally in Lebanon, and a key Tehran demand.

But the president hates to show weakness, particularly if it means abandoning a central objective - which was destroying the mullah’s network of foreign proxies.

Could Trump respond by using military might to reopen the Strait? This seems unlikely. It’s true the US Navy has just escorted a couple of oil tankers out of the Gulf, but that was before the peace talks failed. Getting empty tankers to go back into the Gulf is quite a different proposition, particularly if the Iranians start firing on shipping again.

Might America claim a quick win by seizing Iran’s store of enriched uranium?

It would be no easy matter. According to Trump himself, Iran’s nuclear sites are buried deep below mountains of rubble. Besides there’s little point to such a risky operation. US spy satellites monitor the sites day and night, ensuring the nuclear material remains exactly where it lies.

There are few diplomatic cards to play because, Israel aside, Trump started this war alone.

China would certainly like the crisis to be over because the energy crisis is hitting its trading partners around the world. China pushed Iran to come to the talks in Pakistan, for example.

But Beijing has also been supplying Iran with drones and missile components and many believe its satellite systems are helping Tehran’s missiles find and hit their targets. President Xi Jinping’s reputation for statesmanship grows with every passing day, while Trump’s declines. Only yesterday, one of America’s key Gulf allies, the Crown Prince of the United Arab Emirates, arrived in Beijing for talks. Iran will be the only item on the agenda.

Trump himself is due to visit Xi ‘when the war is over’. He was expecting to arrive in triumph, but at this rate, Trump will be the supplicant.

Another Iran ally, Russia, sees the price of oil soaring - and its coffers swelling. Putin has little incentive to bring the warfare to a halt. No wonder Tehran feels time is on its side.

Not so for Washington. The conflict is already threatening to overshadow the World Cup, which starts on June 11, and America’s 250th birthday celebrations on July 4. Will fears of terrorism haunt Trump’s intended festival of America Made Great Again?

On Saturday, he unveiled plans for a triumphant arch to celebrate US victories over the last 250 years, presumably ending with the conquest of the Islamic Republic of Iran by Donald J. Trump. That triumph is on hold.

Trump has derided his allies’ impotence and, as so often, his jibes are cruelly accurate. For Europe, a cold and expensive winter looms, while the poor in Africa and Asia face hunger as fuel and fertiliser dwindle.

But Trump’s war on Iran has fatally exposed the limits of his own power, too. America’s threats in the Gulf have produced comparatively little. Its standing as the world’s only superpower is fading fast.

Mark Almond is director of the Crisis Research Institute, Oxford